Phase 3: closing-overlay fix + goodbye-composer dedupe

Customer chat refreshSessionStatus now clears sessionExpired carryover so the
goodbye composer renders correctly when re-opening a closing session from
history. Backend /api/shared/chat/:id/info returns goodbye_submitted_by_me;
both apps suppress the composer for the side that has already submitted and
render an awaiting-banner view instead.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/routes/public/shared.chat.routes.js

@@ -1,6 +1,6 @@
 import { authenticate } from '../../plugins/auth.js'
 import { getMessages } from '../../services/chat.service.js'
-import { getSessionClosures } from '../../services/closure.service.js'
+import { getSessionClosures, hasUserSubmittedClosure } from '../../services/closure.service.js'
 import { registerDeviceToken } from '../../services/notification.service.js'
 import { flipSessionSensitivity } from '../../services/sensitivity.service.js'
 import { getDb } from '../../db/client.js'
@@ -55,7 +55,8 @@ export const sharedChatRoutes = async (app) => {
     if (!session) {
       return reply.code(404).send({ success: false, error: { code: 'NOT_FOUND', message: 'Session not found' } })
     }
-    return reply.send({ success: true, data: session })
+    const goodbyeSubmittedByMe = await hasUserSubmittedClosure(sessionId, request.userType)
+    return reply.send({ success: true, data: { ...session, goodbye_submitted_by_me: goodbyeSubmittedByMe } })
   })
 
   // Get full transcript (read-only, for history)